Multi-pyrene assemblies supported on stannoxane frameworks: Synthesis, structure and photophysical studies

Article abstract of DOI:10.1002/asia.201400054

Organostannoxanes have been used as scaffolds for the preparation of multi-chromophore assemblies. A single-step synthesis procedure allows the preparation of compounds in which the number of chromophore units can be varied from two to six. Thus, the reactions of pyrene sulfonic acid (PySO₃H) or C₁₆H₉CHNC₆H₃(COOH)₂ (LH₂) with various organotin precursors gave pyrene-containing organostannoxanes, that is, [Ph₃SnPySO₃]₆ (1), [{(Me₂Sn)₂(μ₃-O)(μ-OH)PySO ₃}₂{(Me₂Sn)₂(μ₃-O) (μ-OH)H₂O}₂?2PySO₃] (2), [{tBu ₂Sn(OH)PySO₃}₂] (3), [{(nBuSn) ₁₂(O)₁₄(OH)₆{PySO₃}₂] (4), and [{(nBu₂Sn)L}₃]₂?C₆H ₅CH₃ (5). Compounds 1-5 were characterized by using X-ray crystallography. Compounds 1 and 5 are 24-membered macrocycles. Macrocycle 1 possesses intramolecular π-π stacking interactions. An unusual co-crystal of two tetrameric ladders in 2 was observed in which one of the components of the co-crystal is neutral whereas the other is dicationic and two pyrenesulfonate counterions are present to balance the overall charge. In the solid state these compounds reveal rich supramolecular structures. Photophysical studies on 1-5 reveal that interactions in the solid state lead to considerable broadening of the emission bands. Ring-tin-tin: The reactions of pyrene sulfonic acid (PySO₃H) or C₁₆H₉CHNC ₆H₃(COOH)₂ (LH₂) with various organotin precursors afforded pyrene-containing organostannoxanes (see figure), such as [Ph₃SnPySO₃]₆ (1), [{(Me ₂Sn)₂(μ₃-O)(μ-OH)PySO₃} ₂{(Me₂Sn)₂(μ₃-O)(μ-OH)H ₂O}₂?2PySO₃] (2), [{tBu₂Sn(OH) PySO₃}₂] (3), [{(nBuSn)₁₂(O) ₁₄(OH)₆{PySO₃}₂] (4), and [{(nBu₂Sn)L}₃]₂?C₆H ₅CH₃ (5) which show interesting photophysical properties.

Full text of DOI:10.1002/asia.201400054

FULL PAPER
DOI: 10.1002/asia.201400054
Multi-Pyrene Assemblies Supported on Stannoxane Frameworks: Synthesis,
Structure and Photophysical Studies
Subrata Kundu,[a] Ramesh K. Metre,[a] Rajeev Yadav,[a] Pratik Sen,[a] and
Vadapalli Chandrasekhar*[a, b]
Abstract: Organostannoxanes have
been used as scaffolds for the prepara-
tion of multi-chromophore assemblies.
H2O}2·2PySO3]
[{tBu2Sn(OH)PySO3}2]
[{(nBuSn)12(O)14(OH)6ACTHNUTRGNE{UNG PySO3}2]
and [{(nBu2Sn)L}3]2·C6H5CH3 (5). Com-
pounds 1–5 were characterized by
using X-ray crystallography. Com-
pounds 1 and 5 are 24-membered mac-
rocycles. Macrocycle 1 possesses intra-
(2),
(3),
(4),
molecular p–p stacking interactions.
An unusual co-crystal of two tetramer-
ic ladders in 2 was observed in which
one of the components of the co-crystal
is neutral whereas the other is dication-
ic and two pyrenesulfonate counterions
are present to balance the overall
charge. In the solid state these com-
pounds reveal rich supramolecular
structures. Photophysical studies on 1–
5 reveal that interactions in the solid
state lead to considerable broadening
of the emission bands.
A
single-step synthesis procedure
allows the preparation of compounds
in which the number of chromophore
units can be varied from two to six.
Thus, the reactions of pyrene sulfonic
acid (PySO3H) or C16H9CHNC6H3
ACHTUNGTRENNUNG
Keywords: cage
compounds
·
macrocycles · photophysical proper-
ties · pyrene · stannanes · supra-
molecular chemistry
2ACHUTGNRENNUG(m3-O)ACHTUTGNRENNNUG
C
E
ACHTUNGTRENNUNG
Introduction
a very interesting class of compounds that have been attract-
ing interest in view of their remarkable structural diversity.[8]
This family of compounds can be prepared either by con-
trolled hydrolysis of organotin halides or by the reactions of
appropriate organotin precursors with protic acids, such as
In recent years, metal-directed coordination-driven self-as-
sembly has become an important tool for construction of
macrocycles, cages, and extended structures.[1] Such com-
pounds with cavities, pores, or channels are of current inter-
est due to their wide range of applications in supramolecular
catalysis,[2] nanomaterials,[3] sorption,[4] and molecular recog-
nition.[5] Furthermore, these compounds can hold functional
moieties that can show redox activity, photophysical proper-
ties, catalytic properties, chemical sensing, and interesting
supramolecular assemblies.[6] Until now such assemblies
have been limited to transition-metal-containing systems be-
cause of their highly directional coordination nature, al-
though a few examples of main-group-containing com-
pounds are now known.[7] Of the main-group-metal-contain-
ing macrocycles, cages, and clusters, organostannoxanes are
carboxylic, phosphonic, phosphinic, or sulfonic acids.[9]
A
large number of structurally diverse organooxotin assem-
blies (such as drums, cubes, O-capped clusters, double-O-
capped cluster, tetranuclear cages, butterfly clusters, hydrox-
yl-bridged dimers, and football cages) have been prepared
and structurally characterized by using relatively simple syn-
thetic methodologies that involve a variation in the nature
of the protic acid/organotin precursor or their stoichiometric
ratio.[10] The rich structural diversity of organostannoxanes
have prompted their utilization as scaffolds for putting to-
gether functionalities that are photo/redox/catalytically
active.[11] The dendrimeric nature of hexameric organostan-
noxanes with a drum structure has allowed manifestation of
cooperative behavior of the functional periphery. For exam-
ple, an extensive cooperative effect between the CuII cen-
ters, in a hexaporphyrin organostannoxane drum, results in
a facile cleavage of supercoiled DNA in an essentially cata-
lytic process.[11a] More recently, organostannoxane-supported
phosphine ligands have enabled the stabilization of Pd0
nanoparticles. Such hybrid systems have been effectively uti-
[a] S. Kundu, R. K. Metre, R. Yadav, Dr. P. Sen, Dr. V. Chandrasekhar
Department of Chemistry
Indian Institute of Technology Kanpur
Kanpur 208016 (India)
Fax : (+91)521-259-0007/7436
E-mail: vc@iitk.ac.in
[b] Dr. V. Chandrasekhar
National Institute of Science Education and Research
Institute of Physics Campus
School of Chemical Sciences
À
lized as catalysts in various C C bond formation reac-
tions.[11c,d] Similarly, O O bond formation mediated by a hex-
À
Bhubaneshwar 751005 (India)
anuclear iron complex supported on a stannoxane core has
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201400054.
also been reported.[11e]
1
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Vadapalli Chandrasekhar et al.
Of the various protic acids that have received attention,
sulfonic acids are the most intriguing because of their weak
coordinating capability. Thus, we have utilized the reactions
of sulfonic acids with organotin substrates to stabilize hy-
drated organotin cations. However, depending on the reac-
tion conditions sulfonate coordination has also been ob-
served that in some instances leads to extended structures.
We were interested in examining if one could utilize the re-
actions of sulfonic acids with organotin substrates to gener-
ate photoactive compounds, particularly because the
number of such photoactive organostannoxane compounds
is extremely limited.[11b] There is also considerable contem-
porary interest in compounds that contain pyrene chromo-
phores.[12] This is due to the fact that such compounds pos-
sess long excited-state lifetimes, high quantum yields, and
exceptional distinction of the fluorescence bands for mono-
mers and excimers.[13] In addition, the favorable redox po-
tential of pyrene is also well suited for semiconductor sensi-
tization.[14] Keeping this background, we embarked on an in-
vestigation of various organotin substrates with pyrene sul-
fonic acid and isolated products of varying nuclearities, the
structures of which ranged from macrocycles to cages:
[Ph3SnPySO3]6 (1), [{(Me2Sn)2
a structural form supported by a sulfonate ligand. Previously
the reactions of (Ph3Sn)2O with PhSO3H and 2,5-Me2-C6H3-
SO3H were investigated; the product isolated in both instan-
ces was a one-dimensional polymer (compounds 6[9c] and
7,[9d] Scheme 2). Representative examples of other types of
products obtained in organotin/sulfonate reactions are sum-
marized in Scheme 2. The 119Sn NMR spectrum of 1 shows
a singlet at d=À236 ppm, which indicates that all the tin
atoms present have similar chemical environments. This
chemical shift is similar to that observed for compounds 6
and 7 shown in Scheme 2. The ESI-MS of 1 revealed that al-
though the parent ion was not detected, fragments due to
one half of the molecule (m/z 1913.1979 [(Ph3Sn)3
AHCTUNGTRENNUNG
(PySO3)3 +H2O+H]+) could be seen (see the Experimental
section and Figure S1 in the Supporting Information).
The 1:1 reaction between Me2SnCl2 and PySO3H in the
presence of triethylamine afforded an unusual co-crystal of
two tetrameric ladders, [{(Me2Sn)2ACHTUGNTRENNUG(m3-O)CAHTUGNTREN(NUGN m-OH)PySO3}2
A
N
ACHTUNGTRENNUNG
of the components of the co-crystal is neutral whereas the
other is dicationic. Overall, to balance the charge, two pyre-
nesulfonate counterions are present. The 119Sn NMR spec-
A
R
2ACHTUNGRTNE{NUNG (Me2Sn)2
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
C6H5CH3(5)
[LH2 =
C16H9CHNC6H3ACHTUNGTRENNUNG(COOH)2],
a
macrocycle that contains
three pyrene units, was assem-
bled in reaction involving
a
(nBu2SnO)n and LH2. Interest-
ingly, 1–5, in which the number
of pyrene units vary from two
to six, have been assembled in
high yields in one-pot reactions.
The synthesis, structural charac-
terization, and photophysical
studies of 1–5 are described
herein.
Results and Discussion
Synthetic Aspects
The reaction of (Ph3Sn)2O with
pyrenesulfonic acid (PySO3H)
in a 1:1 stoichiometric ratio in
boiling toluene for 6 h afforded
the
hexameric
macrocycle,
[Ph3SnPySO3]6 (1) in excellent
yield (Scheme 1). As discussed
below, 1 is a discrete hexameric
24-membered macrocycle. This
is the first instance of such Scheme 1. Synthesis of complexes 1–4.
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Consistent with previous synthetic reports on the isolation
of dicationic macrocycles, in the reactions of [nBuS-
n(O)(OH)]n with sulfonic acids, in the present instance the
reaction of [nBuSn(O)(OH)]n and PySO3H also afforded
[{(nBuSn)12(O)14(OH)6ACHTNUTRGENUNG
{PySO3}2] (4). The 119Sn NMR spec-
trum of 4 displays two signals at d=À281 and À460 ppm,
which are consistent with literature precedents.[10f] The sta-
bility of the structure of 4 in solution is attested by the de-
tection of the parent ion peak in its ESI-MS spectrum at m/
z 2717.6399 [(nBuSn)12(O)14(OH)6ACTHNUTRGNEUNG
(PySO3)]+ (Supporting In-
formation, Figure S2).
Hçpfl and co-workers have previously isolated a tri-tin-
[8f]
containing macrocycle, [nBu2Sn{C6H4-1,3-ACHTUNGRTNEUNG(CO2)2}]3 in the
reaction of [nBu2SnO]n with {C6H4-1,3-(CO2H)2}. We wanted
to use this reaction to create a functional periphery around
the macrocycle. Accordingly the dicarboxylic acid was modi-
fied to C16H9CHNC6H3ACHTNUTRGNE(NUG COOH)2 (LH2), which contained
a pyrene appended through a CH=N linkage. The reaction
of LH2 with [nBu2SnO]n afforded the macrocyle
[{(nBu2Sn)L}3]2·C6H5CH3 (5) as per our expectation
(Scheme 3), which indicates that the synthetic methodolo-
gies utilized in organostannoxane chemistry are quite
robust. Compound 5 is a 24-membered macrocycle that does
not show parent ion peaks in its ESI-MS spectrum. The
Scheme 2. Representative examples of products obtained in the reactions
of organotin substrates with sulfonate ligands.
119Sn NMR of 5 shows a signal at d=À156 ppm that is com-
[8f]
parable to that shown by [nBu2Sn{C6H4-1,3-ACHTNUTRGEN(UNG CO2)2}]3.
trum of 2 displays four signals at d=À142 (s), À148 (s),
À180 (s), and À196 ppm (s), which is indicative of the two
distinct chemical environments present in the two ladder
motifs.
X-ray Crystallography
(Ph3SnPySO3)6 (1)
The reaction between (tBu2SnO)3 and PySO3H in a 1:3
ratio afforded the neutral hydroxide-bridged dimer
[{tBu2Sn(OH)PySO3}2] (3). It is important to note that previ-
ously the reaction between (tBu2SnO)3 and CF3SO3H afford-
ed a cationic complex (compound 8,[9e] Scheme 2). The
119Sn NMR spectrum of 3 shows a singlet at d=À223 ppm.
It is interesting to note that the chemical shifts of 8 and 9[9e]
occur at d=À250 and À188 ppm. However, the chemical
shift of 10[9f] was observed at d=À210 ppm.
The molecular structure of 1 is depicted in Figure 1a. Com-
pound 1 consists of six Ph3Sn fragments linked together by
the anisobidentate bridging coordination of six pyrenesulfo-
nates to afford a hexanuclear 24-membered Sn6O12S6 macro-
cycle. Such a molecular hexameric cluster is unknown in the
organotinsulfonate family. With respect to the mean plane
of the macrocycle, alternate tin atoms lie above and below
the plane (Figure 1b). All the pyrene groups are located on
Scheme 3. Synthesis of complex 5.
3
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The supramolecular structure
of 1 reveals that the pyrene
groups in 1 are involved in an
intramolecular p–p stacking in-
teraction (3.785 ꢁ) with the
phenyl group, which is located
outside
the
macrocycle
(Figure 2). This interaction
could be the one of the driving
forces for the macrocycle for-
mation rather than the 1D poly-
meric chains that were isolated
with other sulfonates. In addi-
tion to the above-mentioned in-
teraction, intermolecular p–p
stacking (3.800 ꢁ) between ad-
jacent pyrene–pyrene rings re-
sults in an aesthetically pleasing
3D structure (Supporting Infor-
mation, Figure S3).
A
R
ACHTUNGERTN(NUNG m-
E
The molecular structure of 2 is
shown in Figure 3. The molecu-
lar structure contains two dif-
ferent hydroxide-bridged tetra-
meric organostannoxane lad-
ders that are co-crystallized
with each other. Such co-crys-
tallization of two ladder motifs
is unprecedented. The core of
the ladder reveals that there
Figure 1. a) Molecular structure of (Ph3SnPySO3)6 (1) and b) the 24-membered macrocycle and the mean
À
plane passing through the tin atoms. c) The geometry around one of the tin atoms. Bond lengths [ꢁ]: Sn1 O1
À
À
À
À
2.341(3), Sn1 O3 2.230(3), Sn1 C1 2.133(4), Sn1 C7 2.124(4), Sn1 C13 2.116(4); bond angles [8]: C13-Sn1-C7
129.02(16), C13-Sn1-C1 115.23(16), C7-Sn1-C1 114.86(16), C13-Sn1-O3 94.75(14), C7-Sn1-O3 94.57(14), C1-
Sn1-O3 89.47(14), C13-Sn1-O1 88.09(14), C7-Sn1-O1 86.03(14), C1-Sn1-O1 86.50(13), O3-Sn1-O1 175.78(10).
d) The deviation of the Sn atoms from the mean plane.
the exterior of the macrocycle. Of the three phenyl substitu-
ents on tin, two are pointed inwards whereas one is pointed
away from the macrocycle. The tin atoms present in 1 are
pentacoordinate in a distorted trigonal bipyramidal geome-
try; each of the tin atoms is bound to three phenyl groups
and two sulfonate oxygen atoms (Figure 1c; t=0.78; the t
values for idealized geometries are t=0, rectangular pyra-
are two distannoxane motifs that are fused to each other to
form a ladder-like structure. Apart from the two hydroxide
bridges (O5 and O7) in the two stannoxane units, there are
two capping (m3-O) oxygen atoms O4 and O6 which also
serve to bridge the stannoxane units. The essential differ-
midal, t=1, trigonal-bipyramidal).[15] The average Sn C
À
À
bond is 2.124(4) ꢁ. The average Sn O bond is 2.285(3) ꢁ.
The O-Sn-O bond angle is 175.78(10)8.
À
Figure 3. Molecular structure of 2. Selected bond lengths [ꢁ]: Sn2 O10
À
À
Figure 2. Intra- and intermolecular p–p stacking interactions.
Chem. Asian J. 2014, 00, 0 – 0
2.803(6), Sn3 O1 2.297(8), Sn2 O8 2.428(7).
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Vadapalli Chandrasekhar et al.
ence between the two tetramers present in 2 is that in one
À
case the sulfonate binds to the terminal tin atoms (Sn3 O1
2.297(8) ꢁ), whereas in other case there is only a weak in-
À
teraction (Sn2 O10 2.803(6) ꢁ) along with a water molecule
coordination to the terminal tin atoms (Figure 3). Thus, one
tetramer is neutral whereas the other is dicationic. All the
tin atoms (Sn1–Sn4) in complex 2 are five-coordinated and
have a distorted rectangular pyramidal geometry (Support-
ing Information, Figure S4).
À
Figure 5. Molecular structure of (3). Bond lengths [ꢁ]: Sn1 O1 2.041(4),
À
À
À
À
Sn1 O1* 2.170(4), Sn1 O2 2.206(6), Sn1 C17 2.159(1), Sn1 C21
2.179(9); bond angles [8]: Sn1-O1-Sn1* 110.35(3), O1-Sn2-O1* 69.65(3),
O2-Sn1-O1 84.54(2), O2-Sn1-O1* 154.29(2), O2-Sn1-C17 92.13(3), C21-
Sn1-C17 126.86(2).
The crystal structure of 2 reveals that each tetramer forms
a 1D hydrogen-bonding chain as a result of intermolecular
À
À
hydrogen bonding (O5 H5O···O2 1.964(1); O7 H7O···O9
1.871(8) ꢁ) between the hydroxide hydrogen and the sulfo-
nate oxygen (Figure 4a). The two resultant parallel 1D
chains are joined together by the another set of intermolec-
À
one monodentate sulfonate ligand (Supporting Information,
Figure S5). The average Sn O bond length found in the
Sn2O2 core is 2.106(8) ꢁ. The average O Sn O bond angle
is 69.7(3)8. The average Sn-O-Sn bond angle within the
Sn2O2 core is 110.3(3)8. The four-membered Sn2O2 ring is
À
À
À
ular
hydrogen-bonding
interactions
(O8 H8A···O11
À
1.958(6); O8 H8B···O3 1.994(7) ꢁ} between the sulfonate
oxygen and the coordinated water to form a 2D supramolec-
ular network (Figure 4b).
À
planar. The average Sn O sulfonate bond is 2.206(6) ꢁ.
Several hydrogen-bonding interactions and other nonco-
valent interactions are present in the crystal structure of 3.
The bridging hydroxide ligands are involved in an intramo-
lecular hydrogen bonding with the S=O unit of the pyrene
sulfonate (Figure 5) to generate a six-membered ring on
either side of the four-membered Sn2O2 ring. Again the two
À
S=O units participate in strong intermolecular C H···O hy-
À
À
drogen bonding (C3 H3···O4 2.691 and C5 H5···O3
À
2.751 ꢁ) with pyrene C H (Figure 6) to form a 1D hydro-
gen-bonding chain. The pyrene units are further involved in
p···p stacking interactions (3.706 ꢁ; Figure 6) which promote
the 2D supramolecular structure formation.
Figure 6. Intermolecular hydrogen bonding and p–p stacking in com-
pound 3.
ACHTUNGERN[UNG {(nBuSn)12(O)14(OH)6ACHTUGNTREN{NUGN PySO3}2] (4)
The molecular structure of 4 is shown in Figure 7. Selected
bond lengths and bond angles are given in Figure S6 in the
Supporting Information. The asymmetric unit contains half
of the molecule. The cationic component of 4 contains
Figure 4. a) 1D hydrogen-bonding array of 2 (methyl groups have been
omitted for clarity) and b) 2D hydrogen-bonding array of 2 (methyl
groups and pyrene moiety have been omitted for clarity).
À
a Sn O-based dicationic Sn12 cage with fourteen m3-O and
ACHTUNGTRENNUNG[{tBu2Sn(OH)PySO3}2] (3)
six m-OH bridges. Of the 12 tin atoms present, six are five-
coordinated with a distorted rectangular pyramidal geome-
try (t=0.46) and the remaining six are six-coordinated with
a distorted octahedral geometry (Supporting Information,
Figure S6). The structure of the cationic tin cage [(nBuSn)12
The molecular structure of 3 is depicted in Figure 5. Com-
plex 3 crystallized as a discrete dimer in which the two tin
atoms are bridged by two hydroxide ligands to generate
a four-membered Sn2O2 ring. Both the tin centers are five-
coordinate in a distorted rectangular pyramidal geometry
(t=0.46) with two tert-butyl groups, two hydroxides, and
(m2-OH)6]2+ is similar to that observed previously.[10f]
ACHUTNGRENU(NG m3-O)14ACHUTNGTRENNGUN
Interestingly, the supramolecular structure of 4 also is very
5
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Vadapalli Chandrasekhar et al.
toluene molecule. Complex 5 is a trinuclear 24-membered
(C15O6Sn3) macrocyclic ring. All 24 atoms of the macrocycle
are in the same plane, which is similar to [nBu2Sn{C6H4-1,3-ACHTUNG-
TERNNUG
(CO2)2}]3.[8f] All six oxygen atoms are oriented towards the
cavity and the six n-butyl groups attached to the tin centers
are approximately perpendicular to the molecular plane.
The tin atoms contain a 4O, 2C coordination. The carboxyl-
ate ligands bind to tin in an anisobidentate-chelating mode
analogous to that observed for [nBu2Sn{C6H4-1,3-ACHTUNGTRENNUNG(-
CO2)2}]3.[8f] A pseudorotaxane structure is observed for 5 as
À
a result of intermolecular C H···O interactions between two
adjacent molecules (Figure 9 and the Supporting Informa-
tion). Unlike [nBu2Sn{C6H4-1,3-ACHTNUGTREN(UNG CO2)2}]3, in the present in-
stance we observed a p–p stacking interaction (3.600 ꢁ) be-
tween the two phenyl groups of the two macrocycles
(Figure 9).
Figure 7. Molecular structure of 4.
close to that reported in previous instances (Supporting In-
formation, Figure S7).[10f]
ACHTUNGTRENNUNG[{(nBu2Sn)L}3]2·C6H5CH3 (5)
The molecular structure of 5 is shown in Figure 8. The asym-
metric unit contains two molecules of compound 5 and one
Figure 9. Pseudorotaxane-type unit in the supramolecular structure of 5.
UV/Vis Absorption and Fluorescence Studies
An investigation of spectroscopic behavior of pyrene-con-
taining organostannoxanes 1–5 along with the ligands
PySO3H and LH2 was carried out. UV/Vis absorption spec-
tra of all the compounds were recorded in DMSO at a con-
centration of 10À6 m (Figure 10). The spectra of all com-
pounds are characterized by the presence of characteristic
strong pyrene p–p* transitions. The absorption spectra of
PySO3H and 1–4 show four absorption bands at l=279, 318,
331, and 349 nm, whereas for LH2 and 5 the absorption
bands were observed at l=292, 380, and 402 nm
(Figure 10). The absorption spectra of LH2 and 5 (broad and
Figure 8. a) Molecular structure of 5 (nBu groups and hydrogen atoms
have been omitted for clarity). b) Coordination environment around an
À
À
À
Sn atom. Bond lengths [ꢁ]: Sn1 O7 2.545(20), Sn1 O8 2.103(19), Sn1
À
À
À
O9 2.102(18), Sn1 O10 2.551(20), Sn1 C92 2.064(34), Sn1 C96
2.108(52); bond angles [8]: O7-Sn1-O8 55.74(7), O9-Sn1-O10 55.49(6),
O8-Sn1-O9 82.42(2), O7-Sn1-O9 138.11(8), O8-Sn1-O10 137.91(7), O7-
Sn1-O10 166.31(6), C92-Sn1-C96 126.79(2).
Figure 10. Absorption spectra of compounds 1–5, PySO3H, and LH2.
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Vadapalli Chandrasekhar et al.
structureless) are redshifted with respect to 1–4 (and
PySO3H), which may be due to the extended conjugation
length of the pyrene chromophore.[14]The intensity of ab-
sorption of 1–4 increases linearly with an increase in the
number of pyrene units on the organostannoxane (Table 1).
Table 1. Quantum yields of 1–5.
Absorbance at
Quantum yield [F]
l=349/379 nm
PySO3H
1
2
3
4
LH2
5
0.04
0.22
0.16
0.091
0.082
0.024
0.075
0.10
0.14
0.11
0.099
0.10
–
0.06
The emission spectra of all the compounds were recorded
by excitation at l=350 nm both in solution (DMSO, 10À6 m)
and in the solid-state (Figures 11 and 12). The emission
spectra of PySO3H and 1–4 showed three emission bands at
Figure 12. Fluorescence emission spectra of LH2 and 5 in a) DMSO and
b) the solid state.
l=365, 369, and 373 nm with a hump at l=380 nm in
DMSO. The emission intensity is higher in 1 followed by 2,
3, 4, and PySO3H.The higher intensity of 1 is due to the
presence of six chromophores. Note that 3 and 4, which con-
tain the same number of chromophores, have a similar emis-
sion intensity. However, in the solid state the interaction of
À
the aromatic units through C H···p and p···p stacking (as
discussed in the crystallographic section) induces partial
pyrene aggregation or preassociation in the ground state
and pyrene excimer formation occurs as noted by the emis-
sion wavelength (l=487 nm).[13a] Interestingly, LH2 and 5
are both comparatively weakly fluorescent compared with
PySO3H and compounds 1 to 4, both in solution and the
solid state, presumably because of subtle change in the ex-
cited-state potential energy surface that lead to an extra
nonradiative pathway in the molecule. Compound 5 has an
emission maximum at l=419 nm in the solution, which is
redshifted, with a broad band at l=548 nm due to excimer
formation in the solid state.
Figure 11. Fluorescence emission spectra of 1–4 and PySO3H in
a) DMSO and b) the solid state.
7
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Vadapalli Chandrasekhar et al.
General synthetic procedure for 1 and 3–5
Conclusion
A stoichiometric mixture of the organotin precursor and the protic acid
were dissolved in toluene (25 mL) and heated under reflux for 6 h. A
small amount of methanol was added to this solution and the mixture
was again heated under reflux for 2 h. It was then filtered and the filtrate
concentrated to 10 mL. Slow evaporation of this concentrate afforded X-
ray quality crystals of 1 and 3–5. Specific details of each reaction are
given below.
Reactions of various organotin substrates with pyrenesulfon-
ic acid and pyrene-functionalized isophthalic acid afforded
compounds with diverse structural forms, the structure of
which appears to depend on the number and nature of tin-
bound organic substituents and the protic acid used. Here
we have demonstrated a simple one-step and highly efficient
approach to the construction of multi-pyrene assemblies. Of
multi-pyrene assemblies 1–5, complexes 1 and 5 are 24-
membered macrocycles that contain six and three pyrene
units, respectively. For the formation of unprecedented mac-
rocycle 1, p–p stacking interactions play an important role
in the self-assembly process. The photophysical studies of 1–
5 reveal a redshift in the emission maxima in the solid state,
as a result of intermolecular interactions. In solution, the
emission intensity can be directly correlated to the number
of pyrene units present in the organostannoxane assembly.
[Ph3SnPySO3]6 (1)
AHCTNUGTREN(GUNN Ph3Sn)2O (0.20 g, 0.28 mmol), PySO3H (0.16 g, 0.56 mmol); yield: 0.32 g
(92%). M.p. >2508C. 1H NMR (500 MHz, (CD3)2SO): d=7.48–7.54 (m,
9H,Ph), 7.68–7.82 (m, 6H, Ph), 8.04 (t, 1H, Py), 8.11–8.18 (m, 4H, Py),
8.25–8.28 (m, 2H, Py), 8.48 (d, 1H, Py), 9.14 ppm (d, 1H, Py);119Sn NMR
(150 MHz, (CD3)2SO): d=À236.0 ppm (s); IR (KBr): n˜ =3043 (m), 3330
(m, br), 1590 (m), 1483 (s), 1433 (s), 1256 (s), 1193 (m), 1110 (s), 997 (s)
1019 (m), 841 (s), 731 (s), 697 cmÀ1 (s); ESI-MS: m/z (%): 1913.1973
[(Ph3Sn)
1280.1238 [(Ph3Sn)
calcd (%) for C204H144O18S6Sn6: C 64.68, H 3.83; found: C 64.20, H 3.88.
3A
(PySO3)2]+(28),
3ACHTUNGTRENNUNG
CTHUNGTRENNUNG
A
2CATHGNUTRENU(NG m3-O)ACHUTTGNNER(NUGN m-OH)PySO3}2AHCTNUTREGNUNNG{(Me2Sn)2AHCTGNUTRNEN(UNG m3-O)ACHTUNGTNRUEGN(m-OH)H2O}2·2PySO3]
Me2SnCl2 (0.20 g, 0.91 mmol) and PySO3H (0.26 g, 0.90 mmol) were
stirred in the presence of triethylamine (1 mL) in methanol at RT for 6 h.
The resulting solution was concentrated and filtered. Slow evaporation of
the solution afforded the corresponding crystalline product (yield: 0.21 g,
74%). M.p. >2508C; 1H NMR (500 MHz, (CD3)2SO): d=0.53 (s, 6H,
Me),0.62 (s, 6H, Me), 8.05 (t, 1H, Py), 8.11–8.20 (m, 4H, Py), 8.26–8.28
(m, 2H, Py), 8.48 (d, 1H, Py), 9.12 ppm (d, 1H, Py); 119Sn NMR
(150 MHz, (CD3)2SO): d=À142 (s), À148 (s), À180 (s), À196 ppm (s);
IR (KBr): n˜ =3309 (s, br), 2920 (m), 1644 (m), 1591 (s), 1193 (s), 1151
(s), 1052 (m), 989 (s), 853 (s) 823 (m), 780 (s), 714 (s), 669 cmÀ1 (s); ESI-
Experimental Section
Reagents and General Procedure
All the reactions were performed under a dry nitrogen atmosphere by
employing standard Schlenk techniques. Solvents were stored over appro-
priate reagents and distilled under nitrogen prior to use. [nBu2SnO]n,
[(Ph3Sn)2O], [nBuSn(O)OH]n, 1-pyrenesulfonic acid, 1-pyrenecarboxal-
dehyde, and 5-aminoisophthalic acid were purchased from Aldrich and
were used as supplied. [tBu2SnO]3 was prepared according to a literature
procedure.[16,17]
MS: m/z (%): 555.0329 [nBu2SnPySO3HACTHNUTRGNEUNG
(CH3CN)]+ (10); elemental anal-
ysis calcd (%) for C80H92O22S4Sn8: C 38.69, H 3.73; found: C 38.20, H
3.78.
Instrumentation
1H and 119Sn NMR spectra were recorded by using a JEOL JNM Lambda
spectrometer operating at 500.0 and 150.0 MHz respectively. The chemi-
cal shifts are referenced with respect to tetramethylsilane (for 1H) and
tetramethyltin (for 119Sn). High-resolution ESI-MS spectra were recorded
by using a MICROMASS QUATTRO II triple quadrupole mass spec-
trometer. DMSO was used as the solvent for the ESI-MS studies. IR
spectra were recorded as KBr pellets by using a Bruker Vector 22 FTIR
spectrophotometer operating between 400 and 4000 cmÀ1. Melting points
were recorded by using a JSGW melting point apparatus and are uncor-
rected. The steady-state absorption and emission spectra of sample solu-
tions were recorded by using a commercial UV/Vis spectrophotometer
(UV-2450, Shimadzu, Japan) and a spectrofluorimeter (FluoroLog 3-21,
JobinYvon), respectively. The quantum yield measurements were per-
formed using anthracene as the reference.[18] Elemental analyses were
carried out by using a Thermoquest CE instruments model EA/110 CHN
elemental analyzer. TGA measurements were carried out by using
a Perkin–Elmer Pyris6 thermogravimetric analyzer at a heating rate of
108CminÀ1 under an argon atmosphere.
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(88%). M.p. >2508C; 1H NMR (500 MHz, (CD3)2SO): d=1.19 (s, 36H,
tBu), 8.11(t, 2H, Py), 8.11–8.20 (m, 8H, Py), 8.26–8.26 (m, 4H, Py), 8.48
(d, 2H, Py), 9.09 ppm (d, 2H, Py); 119Sn NMR (150 MHz): d=À223 ppm
(s); IR (KBr): n˜ =3039 (m, br), 2961 (m, br), 2856 (m), 1592 (m), 1467
(m), 1369 (m), 1274 (s), 1196 (m), 1085 (s) 1062 (m), 986 (s), 849 (m),
756(m), 711 (m), 663 cmÀ1 (s); ESI-MS: m/z (%): 793.1304 [(tBuS-
n)2(OH) (CH3O)
C48H56O8S2Sn2: C 54.26, H 5.31; found: C54.03, H 5.43.
(PySO3)]+ (76); elemental analysis calcd (%) for
ACHTUNGTRENNUNG
ACHTUNGERN[UNG {(nBuSn)12(O)14(OH)6ACHTUGNTREN{NUGN PySO3}2] (4)
nBuSn(O)OH (0.20 g, 0.96 mmol), PySO3H (0.045 g, 16 mmol); yield:
0.18 g (77%). M.p. >2508C; 1H NMR (500 MHz, CDCl3): d=0.85–0.96
(m, 30H, nBu), 1.33–1.77 (m, 24H, nBu), 7.97–8.19 (m, 7H, Py), 8.67 (d,
1H, Py), 9.20 ppm (d, 1H, Py); 119Sn NMR (150 MHz, CDCl3): d=À281
(s), À460 ppm (s); IR (KBr): n˜ =3243 (m, br), 2936 (s), 2738 (m, br),
2677 (m), 2491 (s), 1640 (w), 1586 (w), 1475 (m), 1433 (m), 1383 (m)
1203 (s), 1185 (s), 1161 (s), 1089 (s), 1036 (s), 852 (s), 843 (s), 677 (s),
617 cmÀ1 (s); ESI-MS: m/z (%): 2717.6399 [(nBuSn)12(O)14(OH)6
Synthesis
AHCTUNGTRENNUNG
(PySO3)]+ (6), 1219.3080 [(nBuSn)12(O)14(OH)6]2+ (10); elemental analy-
Synthesis of [C16H9CHNC6H3ACTHNUTRGEN(UGN COOH)2] (LH2)
sis calcd (%) for C80H132O26S2Sn12: C 32.04, H 4.44; found: C32.34, H
4.49.
A mixture of 5-aminoisophthalic acid (1.00 g, 5.50 mmol) and 1-pyrene-
carboxaldehyde (1.27 g, 5.50 mmol) in CH3OH (30 mL) was heated
under reflux for 6 h. A yellow product formed in the reaction was sepa-
rated by filtration and washed with methanol and toluene to give the
pure product (yield: 2.0 g, 92%). 1H NMR (500 MHz, (CD3)2SO): d=
8.11–8.56 (m, 10H), 8.80 (d, 1H), 9.31 (d, 1H), 9.7 ppm (s, 1H); IR
(KBr): n˜ =2820 (m, br), 2553 (s), 1691(s), 1613(m), 1578 (s), 1321 (m),
1276 (s), 964 (w), 906 (w), 884 (s) 755 (s), 715 (m), 694 (m), 672 cmÀ1
AHCUTNERTGN[GUNN {(nBu2Sn)L}3]2·C6H5CH3 (5)
nBu2SnO (0.20 g, 0.81 mmol), LH2 (0.32 g, 0.81 mmol); yield: 0.49 g
(95%). 1H NMR (500 MHz, CDCl3): d=0.87–0.95 (m, 18H, nBu), 1.42–
1.51 (m, 12H, nBu), 1.78–1.84 (m, 12H, nBu),1.88–1.91 (m, 12H,
nBu),8.06–8.39 (m, 10H), 8.75 (d, 1H), 9.21 (d, 1H), 9.6 ppm (s, 1H);
119Sn NMR (150 MHz, CDCl3): d=À156 ppm (s); IR (KBr): n˜ =3041 (w,
(w); ESI-MS: m/z (%): 394.1078 [M+H]
+A
CHTUNGTRNE(NUNG 100).
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Vadapalli Chandrasekhar et al.
Table 2. Crystallographic data and refinement parameters for 1–5.
1
2
3
4
5
formula
Mr
T [K]
l [ꢁ]
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
C
204H144O18S6Sn6
C80H92O22S4Sn8
2483.50
100(2)
C48H56O8S2Sn2
1062.49
100(2)
0.71073
monoclinic
P21/c
9.147(1)
14.832(1)
17.170(2)
90
97.366(2)
90
C80H132O26S2Sn12
2998.52
100(2)
0.71069
monoclinic
P21/n
12.813(5)
28.030(5)
13.833(5)
908
98.408(5)
90
C205H194N6O24Sn6
3837.93
100(2)
3787.88
100(2)
0.71073
hexagonal
0.71069
0.71073
triclinic
triclinic
¯
¯
¯
R3
P1
P1
34.5428(6)
34.5428(6)
11.3701(6)
90
90
120
11749.2(11)
3
1.606
8.788(5)
13.590(5)
18.612(5)
79.970(5)
83.824(5)
85.686(5)
2172.5(16)
1
17.1099(8)
21.1390(9)
25.5146(11)
78.6020(10)
88.9010(10)
68.0480(10)
8375.2(6)
2
g [8]
V [ꢁ3]
Z
2310.1(4)
2
1.527
4915(3)
2
2.026
1calcd [MgmÀ3
]
1.898
1.522
absorption coefficient 1.095
[mmÀ1
(000)
2.426
1.223
3.102
0.956
]
F
G
5724.0
1408.0
0.16ꢂ0.14ꢂ0.13
1.12–25.50
1080.0
0.13ꢂ0.12ꢂ0.11
1.20–25.50
2904.0
0.16ꢂ0.13ꢂ0.12
1.45–25.50
3916.0
0.025ꢂ0.021ꢂ0.017
2.00-25.50
crystal size [mm3]
q range [8]
0.17ꢂ0.15ꢂ0.13
1.18–25.50
index ranges
À41< =h< =37
À41< =k< =41
À13< =l< =12
21439
4864 [Rint =0.0770]
100.0
À10< =h< =10
À16< =k< =16
À17< =l< =22
11820
7897 [Rint =0.0242]
97.5
À10< =h< =11
À13< =k< =17
À20< =l< =14
12423
4291 [Rint =0.0676]
99.9
À15< =h< =15
À33< =k< =33
À16< =l< =11
26679
9123 [Rint =0.0751]
99.6
À20< =h< =20
À25< =k< =25
À30< =l< =30
80151
31177 [Rint =0.1622]
100.0
reflns collected
independent reflns
Completeness to q
[%]
absorption correction
empirical
empirical
empirical
empirical
empirical
max./min. transmission 0.790/0.742
refinement method Full-matrix least-
squares on F2
0.718/0.672
0.874/0.853
0.689/0.623
0.984/0.977
Full-matrix least-
squares on F2
7897/7/531
Full-matrix least-
squares on F2
4291/0/281
Full-matrix least-
squares on F2
9123/41/541
Full-matrix-block least-
squares on F2
31177/122/2183
data/restraints/parame- 4864/0/352
ters
GOF on F2
1.051
1.136
1.083
1.036
1.006
final R indices
[I>2s(I)]
R indices (all data)
R1 =0.0410
wR2 =0.0900
R1 =0.0597
wR2 =0.1074
R1 =0.0501
wR2 =0.1353
R1 =0.0639
wR2 =0.1944
2.647/À1.991
R1 =0.0461
wR2 =0.0929
R1 =0.0759
wR2 =0.1238
1.954/À0.651
R1 =0.0628
wR2 =0.1471
R1 =0.1073
wR2 =0.1767
2.727/À1.500
R1 =0.0829
wR2 =0.1633
R1 =0.2148
wR2 =0.2114
2.072/À1.469
largest diff. peak/hole 2.030/À0.686
[eꢁÀ3
]
br), 2956 (s), 2924 (m, br), 2856 (m), 1620 (s), 1564 (s), 1401 (m), 1345
(s), 1244 (m), 966 (w) 848 (s), 775 (s), 714 (s), 683 cmÀ1 (s); elemental
analysis calcd (%) for C205H194N6O24Sn6: C 64.15, H 5.09, N 2.19; found:
C 63.85, H 5.13, N 2.15.
Acknowledgements
We thank Department of Science and Technology, India for financial sup-
port. S.K. is thankful to the CSIR, India and R.K.M. and R.Y. are thank-
ful to UGC, India for a Senior Research Fellowship. V.C. is thankful to
the Department of Science and Technology, New Delhi, for the award of
the National J. C. Bose Fellowship.
X-ray Crystallography
Suitable crystals for single-crystal X-ray diffraction measurements were
mounted on a CCD Bruker SMART APEX (for 1, 3, and 5} or a D8
QUEST (for 2 and 4) diffractometer.[19] Data were collected at 100(2) K
by using graphite monochromated MoKa radiation (la =0.71073 ꢁ for 1,
3, and 5 and la =0. 71069 ꢁ for 2 and 4). The structures were solved by
direct methods and refined (SHELXL 97) by full-matrix least-squares
procedures on F2. The hydrogen atoms were included in idealized posi-
tions and were refined according to a riding model. Nonhydrogen atoms
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Received: January 11, 2014
Published online: && &&, 0000
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Chem. Asian J. 2014, 00, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPER
Ring-tin-tin: The reactions of pyrene
Supramolecular Chemistry
sulfonic acid (PySO3H) or
C16H9CHNC6H
G
Subrata Kundu, Ramesh K. Metre,
Rajeev Yadav, Pratik Sen,
Vadapalli Chandrasekhar* &&&& — &&&&
various organotin precursors afforded
pyrene-containing organostannoxanes
(see figure), such as [Ph3SnPySO3]6 (1),
Multi-Pyrene Assemblies Supported
on Stannoxane Frameworks: Synthesis,
Structure and Photophysical Studies
[{(Me2Sn)
{(Me2Sn)2A(m3-O)
(2), [{tBu2Sn(OH)PySO3}2] (3),
[{(nBuSn)12(O)14(OH)6A{PySO3}2] (4),
2A
A
U
and [{(nBu2Sn)L}3]2·C6H5CH3 (5)
which show interesting photophysical
properties.
11
&
&
Chem. Asian J. 2014, 00, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ